Residential solar power systems - how to heat water in your home using alternative solar energy

Introduction

Recent
improvements in the design of solar hot water technology has made it
a much more interesting and affordable option for those who want to
reduce both their heating bills, hot water bills and carbon
footprint.

It
is no longer necessary to live in the Caribbean or in Africa to
install an economic solar hot water system.

For example, throughout
the UK, with modern solar hot water systems it is economical and
cheaper over a number of years to use a solar hot water heater than a
conventional one powered by electricity or by gas.

This article explains how solar energy can be used to heat water in your home, and sets out the main types of residential solar power systems available.

It also provides diagrams and videos for those main types of system, and a guide to working out whether it is worh it financially to install solar powered water heaters.

Average solar irradiance across the world, show in watts per square metre per 24 hours

How residential solar power systems work to heat water in your home

A
solar hot water installation in a residential building usually
consists of solar panels to collect the sun’s energy, and a system
to move the heat from the solar collector to a tank where it can be
used.

Solar
panels are usually put on the roof of a building because that enables
the most energy to be collected by the panels.

A
solar thermal collector which collects the sunlight in order the heat
the water is a much more simple type of technology than panels which
collect sunlight in order to generate electricity.

Many
solar hot water systems in most of the world will need a back-up
energy source, particular in winter when sunlight is uncommon and the
days are short.

Solar hot water systems use both direct and defused
sunlight, so the sunlight doesn’t need to be shining directly on
your collector at all times in order to heat your water.

Different types of solar power water heaters

There
are two main types of solar hot water residential systems.

The first
is a compact or passive system, and is simpler to install and more basic in design (and therefore cheaper) but is less efficient in collecting the sun's energy and does not cope well with cold weather.

The second is an active system, which is more expensive, more complicated, but more efficient and better able to cope with freezing conditions

Passive solar powered water heaters

In
a passive system, there is no external energy input such as
electricity to pump water around.

The first type of passive system
is an integral collector. In this type the water tank is both the
storage place for hot water and the place that collects the sunlight
to heat it.

It is in effect a large water tank on the roof of a
house where the water inside it is heated by sunshine.

They are not
particularly suitable in climates without good and constant sunshine
or in places where it can get cold. They are simpler and cheaper to
run than other systems, but are less efficient.

In
a Thermosyphon, the water tank is installed higher than the collector
for the solar energy. Warm water rises after being heated, and cold
water sinks back into the collecting panels.

Again, this is not a
great system unless you live in a very hot place and there are risks
if the temperature drops below freezing.

In addition, if it gets
really cold at night even if not freezing, the process can go into
reverse and water flows from the tank into the solar panels.

It is
again, a cheap and reliable solution so long as you live in a
reliably sunshiny place.

Active solar powered water heating systems

Active
systems pump and control the hot water, and do generally use
electricity to do so.

This slightly reduces energy saving and carbon
footprint saving, but the systems are generally far more efficient
and better able to cope with cold weather.

In
active systems, the tank is inside the building and water is pumped
from the solar energy collection panels to the tank as it heats up.

Many of these systems are a closed loop, which means that they use a
heat exchange.

This means that the solar panel system and the fluid
in it is sealed, and the water in the tank is not heated directly by
the sunshine but the heat is transferred from the fluid heated by the
sun into the water in the tank.

This has advantages, as antifreeze
can be put in the closed loop, and there is less of a risk of
limescale and other gunk building up in the closed loop system as the
fluid is not continuously replaced.

How to tell how efficient a particular solar energy water heater is

Solar
Energy Factor (SEF) is defined as the amount of energy released by a
system divided by the energy put into the system to run it,
electricity or gas.

The higher the number the more energy efficient
the system is, and energy factors of at least 2 or 3 should be looked
for.

There are also Solar Fraction (SF) ratings. The Solar Fraction
is the proportion of the total conventional hot water heating load
(delivered energy in tanks standby losses).

The higher the Solar
Fraction the greater the solar energy contribution to your water
heating, and the less other energy is needed in back-up water
heaters.

You should be looking for 0.5 to 0.75 solar factor when
choosing a heater.

Back-up systems for solar powered water heaters

If
you buy a residential solar power system for heating water, you must be prepared for times when there will not be enough sunshine to heat the water properly.

It is
generally the case that they either use your existing home system as
back-up for when the weather is not suitable, or include an immersion
switch on the solar tank, or have a type of combination boiler which
heats hot water on demand when the water heated by solar energy is
too cool.

Working out whether it is economical to use solar energy

In
many western countries, there are significant tax breaks and
incentives for installing green types of energy.

When considering
the cost of installing a residential solar energy system, you should
check out and include in your calculations any tax you can reclaim or
subsidies which are applied by local or national government.

In
order to work out how much of your hot water can be generated in your
specific house, taking into account where the panels could be located, you will need to get a quote of the estimated
energy which could be generated from a particular system on your
house per year.

Obviously these estimates can’t be exact, as it
depends on the sunshine. Solar energy providers in the UK tend to
give a range of plus or minus 20%.

This will give you an idea of
whether it’s economically worthwhile to do it.

Comments

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sending

poetryman6969 3 years ago

When I lived in New Mexico, the air was so dry that you could cool a dwelling by what was called "swamp coolers". They cool the air by evaporation. I never looked into it when I was there but I imagine that all over the southwest that solar water heating could be a good way to go.

Alan Bowman 6 years agofrom The World

Your hub was so prescient when you look around you now and have voted it up useful interesting and awesome.

Keep spreading the message.

Kind regards

Alan

Sally Branche 7 years agofrom Only In Texas!

I sure wish we had more solar water heaters here in the US! Voted up and useful! :)

Author

LondonGirl 8 years agofrom London

Couldn't agree more with you.

DIYSolarEnergy 8 years agofrom USA

Great hub on solar water heating...it's time to stop relying sooo much on fossil fuels and take advantage of a natural resource.

Author

LondonGirl 9 years agofrom London

Not exactly lazy, there's a fair amount of stuff about at the moment!

Susan Keeping 9 years agofrom Kitchener, Ontario

Excellent hub. I'm a bit late reading through the hubs...been a little busy :)

Author

LondonGirl 9 years agofrom London

It would indeed - my next solar hub, to be found here, gives the details of generating electricity at home using solar power:

I'd think it'd be feasible to have additional solar panels to generate the electricity to run the pump for the active solar water heating system. ???

Author

LondonGirl 9 years agofrom London

Hi Brian - even in the UK, not top of anyone's list for constant sunshine, these are becoming economical.

NMS - I agree, it's an important source of green energy.

nms 9 years agofrom Cochin

save earth..promote solar enery source

Brian Stephens 9 years agofrom Castelnaudary, France

Very useful information and something I really need to look into, energy costs using fossil fuels are rising exponentially so apart from the fact they are not considered environmentally friendly they really are expensive. This has to mean that the break even point of installation costs versus operational savings must be coming down with respect to time.

Author

LondonGirl 9 years agofrom London

Sounds like a great place for solar energy, then! This hub is only on hot water - other uses of solar energy coming soon.

Sheila 9 years agofrom The Other Bangor

I'm bookmarking this one to come back to. I have got to get solar panels for my house -- it's kinda criminal that I don't already have them. The sun shines here all day every day 355 days of the year.

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